1. Field of the Invention
The invention relates to an anti-static composition, to a process for preparing such composition and to moulded articles comprising anti-static compositions, such as mechanical components.
2. Description of Prior Art
It is known to use electroconductive carbon black in anti-static resin compositions comprising polyoxymethylene (POM) and an epoxy resin compound. Such compositions preferably comprise also an additive for curing the epoxy resin.
It is furthermore known to use carbon fiber for manufacturing an electroconductive composition having a relatively high tensile strength by mixing a carbon fiber with a specific surface layer together with any one of a wide range of thermoplastic resins, including polyoxymethylene.
Significant disadvantages of such known compositions are their less than optimal processability and resulting electrical-, mechanical- and/or thermal properties. For example, the use of carbon black in polyoxymethylene-containing compositions results in less favorable thermal conductivity compared with virgin resin, in particular since relatively large amounts of carbon black have to be used to obtain the desired electroconductivity. Epoxy resins are not reacting in a favourable manner when extrusion of the compositions is envisaged, which is an efficient method of obtaining homogenous compositions comprising POM resins.
Moreover, although the addition of carbon fiber is known to increase the tensile strength of a resin composition, the processability of compositions containing substantial amounts (e.g. 15-20% by weight or more) of carbon fiber in order to make an inherent insulator such as POM resin electroconductive, is not very good, in particular when moulding applications are envisaged.
It would be of substantial interest to manufacturers of anti-static compositions and electrical- or mechanical components made therefrom, if resin compositions would be available which possess both excellent electrical- and mechanical properties and can be processed in equipment normally used therefor.
Surprisingly, it has now been found that anti-static compositions with such desired properties can be obtained by combining a relatively small fraction of carbon fiber with a polyoxymethylene polymer.